The Living Desert
While the Mojave Wasteland is an inhospitable desert full of violent wildlife, murderous raiders, and plenty of other dangers, many people felt the world was too empty when New Vegas released. The Living Desert completely changes that by adding hundreds of NPCs, scripted events, and quest-related events to the game. The entire wasteland feels so much more populated, and the NCR-Legion conflict looms ever closer with the addition of new spawn locations for NCR Troopers and Legionaries, especially at certain locations where their spawns pit them directly into a skirmish.
Not only does this mod flesh out the wasteland with a cast of extra faces, but it also adds many events that are linked to quest outcomes. There are quests now that, if you fail them or resolve them in a way that a certain faction does not like, you will find yourself hunted down by a squad of assassins, determined to put down Courier 6 before they can do any more harm.
Overall, the mod adds incredible depth to the wasteland, and sometimes truly displays the consequences of certain quest outcomes. Doing things for the NCR that directly hurt the Legion can spawn Legion hit squads, or working helping factions regain a foothold in the wasteland can set up checkpoints or prepare ambushes for their enemies. The Living Desert mod is available now on the Fallout: New Vegas Mod Nexus.